1. Field of the Invention
This invention relates to a load bearing structural support for machinery, in particular for damping vibration and shock.
2. Description of the Prior Art
Machinery and the like having rotating and/or cyclically moving components generally cause vibration and fatigue problems resulting from the vibration. Many different types of vibration damping devices have been contemplated in the past to reduce unwanted transmission of vibration. Typical devices for reducing vibration include rubber isolation mounts and the like mounted directly under machinery.
Rubber isolation mounts and the like, due to their material characteristics and the structural arrangement, can only support relatively small loads which limit their utility to small machinery such as pumps and small motors. Since the rubber isolation mounts can only support relatively small loads, other supports must be contemplated for heavy machinery.
Constraining layer damping devices, for example, as shown in FIG. 1, consisting of a layer of viscoelastic material 10, such as rubber, sandwiched between a thick, rigid structural base plate 11 and a stiff constraining layer 12 have been contemplated in the past to reduce vibration where the structural load from machinery 13 is significant or aero/hydro-dynamic surfaces, such as for a propeller blade, are required. The viscoelastic material 10 is bonded to the base plate 11 and the constraining layer 12 is bonded to the viscoelastic material 10. In this type of arrangement, when the support is set into vibration, bending occurs. By virtue of the difference in the stiffnesses between the viscoelastic material and the base plate and the constraining layer, significant shear occurs in the viscoelastic material. It is this shear of the viscoelastic material that dissipates the mechanical vibration.
The constraining layer damping devices, however, have a drawback, in that, the bond line between the viscoelastic material and the base plate and the constraining layer must be constantly maintained in order for the damping to occur. Over a period of use, due to vibration and heat generated by machinery, the bond line will degrade, and therefore the damping provided by this configuration will become inadequate.
U.S. Pat. No. 4,954,377 issued to Fischer, et al., discloses a load damper for service in tensile, compression and torsion as a shock and vibration isolation mounting device. The load damper in U.S. Pat. No. 4,954,377, however, is constructed of a multidimensionally braided textile and a viscoelastic material disposed in the interstrand spaces of the textile. The disclosure of the construction of the multidimensionally braided textile with viscoelastic material described in U.S. Pat. No. 4,954,377 is incorporated herein by reference. Multidimensionally braided or weaved textile is also well known in the trade of producing rigid composites using epoxy, fiberglass and the like, for example, described in Report DTNSRDC/SME-84-86 published in October 1984 by the David Taylor Naval Ship Research and Development Center, entitled "The Fabrication, Processing and Characterization of Multidimensionally Braided Graphite/Epoxy Composite Materials" authored by Aleksander Macander, Roger Crane and Eugene Camponeschi. U.S. Pat. Nos. 3,426,804 issued to Bluck and 4,312,261 to Florentine describe a device for producing a multidimensionally braided preform. Three dimensional braiding is also described in the article "AUTOMATIC THROUGH-THE-THICKNESS BRAIDING" by Richard T. Brown and Eddie C. Crow, Jr of Atlantic Research Corporation, Alexandria, Va., 37th International SAMPE Symposium, Volume 37, pp 832-842, Mar. 9-12, 1992 (hereafter SAMPE article), in which the three-dimensional braiding is capable of automatic fabrication of complex structural shapes such as I-beams, ribs, and blade stiffened panels.